Once you have the fishing pole and the worms, you can go to the pond and fish. Remember to have a slot open in your bag, to hold the fish. When you fish, a transparent fish will appear above a sliding progress-like bar. The goal is to keep the needle underneath the fish, using the space bar. As you line up the needle with the fish, the fish starts turning opaque. At some point, you bag it. Unlike the other harvesting mechanisms, once you bag a fish, the interface will drop you out and you have to press 1 again to keep fishing.